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docs: use let/const instead of var
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@ -28,7 +28,7 @@ function add(x, y) {
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return x + y;
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}
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var numbers = [4, 38];
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const numbers = [4, 38];
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add(...numbers) // 42
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```
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@ -38,7 +38,7 @@ add(...numbers) // 42
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```javascript
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function f(v, w, x, y, z) { }
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var args = [0, 1];
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const args = [0, 1];
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f(-1, ...args, 2, ...[3]);
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```
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@ -74,7 +74,7 @@ f.apply(null, args);
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function f(x, y, z) {
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// ...
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}
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var args = [0, 1, 2];
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let args = [0, 1, 2];
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f(...args);
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```
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@ -102,8 +102,8 @@ var arr2 = [3, 4, 5];
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Array.prototype.push.apply(arr1, arr2);
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// ES6 的写法
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var arr1 = [0, 1, 2];
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var arr2 = [3, 4, 5];
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let arr1 = [0, 1, 2];
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let arr2 = [3, 4, 5];
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arr1.push(...arr2);
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```
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@ -185,8 +185,8 @@ const [first, ...middle, last] = [1, 2, 3, 4, 5];
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JavaScript 的函数只能返回一个值,如果需要返回多个值,只能返回数组或对象。扩展运算符提供了解决这个问题的一种变通方法。
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```javascript
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var dateFields = readDateFields(database);
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var d = new Date(...dateFields);
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let dateFields = readDateFields(database);
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let d = new Date(...dateFields);
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```
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上面代码从数据库取出一行数据,通过扩展运算符,直接将其传入构造函数`Date`。
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@ -236,8 +236,8 @@ str.split('').reverse().join('')
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任何 Iterator 接口的对象(参阅 Iterator 一章),都可以用扩展运算符转为真正的数组。
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```javascript
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var nodeList = document.querySelectorAll('div');
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var array = [...nodeList];
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let nodeList = document.querySelectorAll('div');
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let array = [...nodeList];
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```
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上面代码中,`querySelectorAll`方法返回的是一个`nodeList`对象。它不是数组,而是一个类似数组的对象。这时,扩展运算符可以将其转为真正的数组,原因就在于`NodeList`对象实现了 Iterator 。
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@ -275,7 +275,7 @@ let arr = [...map.keys()]; // [1, 2, 3]
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Generator 函数运行后,返回一个遍历器对象,因此也可以使用扩展运算符。
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```javascript
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var go = function*(){
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const go = function*(){
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yield 1;
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yield 2;
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yield 3;
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@ -289,7 +289,7 @@ var go = function*(){
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如果对没有 Iterator 接口的对象,使用扩展运算符,将会报错。
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```javascript
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var obj = {a: 1, b: 2};
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const obj = {a: 1, b: 2};
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let arr = [...obj]; // TypeError: Cannot spread non-iterable object
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```
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@ -356,7 +356,7 @@ Array.from([1, 2, 3])
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```javascript
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// arguments对象
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function foo() {
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var args = [...arguments];
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const args = [...arguments];
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}
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// NodeList对象
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@ -517,7 +517,7 @@ Array.prototype.copyWithin(target, start = 0, end = this.length)
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// {0: 1, 3: 1, length: 5}
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// 将2号位到数组结束,复制到0号位
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var i32a = new Int32Array([1, 2, 3, 4, 5]);
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let i32a = new Int32Array([1, 2, 3, 4, 5]);
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i32a.copyWithin(0, 2);
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// Int32Array [3, 4, 5, 4, 5]
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